Various unvented gas heaters are found in the prior art. One such type of heater is found in U.S. Pat. No. 2,696,205, issued to Ruhl on Dec. 7, 1954. This patent is directed to a space heater which is positioned in a room to provide heat thereto. The heater includes a housing enclosing a combustion chamber wherein gas is ignited. The gas heats surrounding gridwork of the structure, and air is allowed to circulate over this heated fixed gridwork and escape into the immediate area of the heater for heating thereof. The heater does not include ducts or forced air to distribute air out of the heater, and no enclosure, such as a fireplace, is provided around the heater. Furthermore, no suggestion is made of the use of gas logs in the combustion chamber.
Applicant has provided an unvented gas-fired heater which is easily insertable into various enclosures, such as fireplaces. The heater utilizes gas logs in the combustion area to create a much greater heating surface than can be found in the U.S. Pat. No. 2,696,205. The fireplace provides a warm enclosure for the heater by retaining a large amount of heat generated in the heater combustion chamber in the immediate surrounding area of the heater. An adjustable duct assembly provides for efficient heat distribution from the heater while permitting the heater to be mounted in different sized enclosure openings.